1. Field of the Invention
The present invention relates to an electrostatic discharge protection device. More particularly, the present invention relates to an electrostatic discharge protection device for providing an electrostatic discharge path between two circuitries.
2. Descriptions of the Related Art
An electrostatic discharge phenomenon releases energy to a circuitry, causing a temporarily high voltage and current in the circuitry. This high voltage and current may damage the circuitry in a chip. For example, it may damage internal circuits, or the internal conducting wire. Thus, it is important to provide a non-damaging electrostatic discharge path between internal circuits.
Conventional solutions have placed power cut cells between two internal circuits. The power cut cell is generally a power cut diode combination comprising two power cut diode modules configured to conduct in contrary directions. The combination can be set between two power supply terminals or two ground terminals, as shown in FIG. 1.
FIG. 1 shows two power cut diode combinations 11, 12. The power cut diode combination 11 connects power supply terminals VCC1 and VCC2, while the power cut diode combination 12 connects ground terminals GND1 and GND2. The power cut diode combination 11 comprises two power cut diode modules 111 and 112 configured to conduct in contrary directions. In addition, the power cut diode combination 12 comprises two power cut diode modules 121 and 122 configured to conduct in contrary directions. The power supply terminals and ground terminals respectively connect with the electrostatic discharge (ESD) protection device (not shown in FIG. 1) for conducting ESD energy out of the circuitry. Meanwhile, the turn-on voltage of the diode can block noise flowing between the two internal circuits when the power cut diode is not turned on.
The operations of the power cut diode combinations 11, 12 are described as follows. When an ESD phenomenon occurs on the VCC1, a temporary high voltage occurs. At this time, an ESD protection device connected to the VCC1 forces the ESD energy out of the circuitry. In addition, the power cut diode module 111 guides the ESD energy to the VCC2, so an ESD protection device connected to the VCC2 can force the ESD energy out of the circuitry jointly. By the same principle, when the ESD phenomenon occurs on the VCC2, the power cut diode module 112 can guide the ESD energy to the VCC1. The power cut diode combination 12 operates in a similar way and forces the ESD energy out of the circuitry.
The equivalent model of a diode can be simply realized as combination of an ideal diode and an internal resistor in series, as shown in FIG. 2. FIG. 2 shows an ideal diode 21 and an internal resistor 22 in series, where the ideal diode 22 has an input 211 and an output 212. The ideal diode 21 is presumed to have a threshold voltage without an internal resistor. When the differential voltage caused by the input 211 and the output 212 is higher than the threshold voltage, the ideal diode 21 turns on, and the current flows through the internal resistor 22 and out the output 212. Thus, when the electrostatic discharge energy turns on the ideal diode 21, a voltage is produced by the two ends of the internal resistor 22 due to the flowing current. As a result, the electrostatic discharge energy is more or less blocked by the internal resistor 22. However, there are drawbacks of applying a combination of power cut diodes as a power cut cell.
The aforementioned drawbacks would diminish electrostatic discharge protection. However, conventional technology is not capable of providing a power cut cell that has a low internal resistor when it turns on, and blocks the noise when it turns off.
Therefore, an electrostatic discharge protection device with a low internal resistor and a noise blocking ability is needed in the semiconductor industry.